Method for connecting at least two components using a sintering process

ABSTRACT

The invention relates to a method for connecting at least two components ( 18, 20 ) using a sintering process. The aim of the invention is to improve the sintering process. This is achieved in that the method has the following method steps: a) providing a starting material ( 10 ) of a sintering compound ( 22 ), comprising particles ( 12 ) which can be sintered and have at least one metal or at least one metal compound and comprising at least one polymeric, polymerizable, and/or monomeric organic compound ( 14 ), wherein the polymeric, polymerizable, and/or monomeric compound ( 14 ) has a flow temperature which is higher than or equal to the room temperature and lower than the sintering temperature, and the polymeric, polymerizable, and/or monomeric organic compound ( 14 ) further has a desorption temperature which is higher than the flow temperature and lower than or equal to the sintering temperature; b) arranging the starting material ( 10 ) between two components ( 18, 20 ) to be connected; c) heating the starting material ( 10 ) to a temperature (T 1 ) which is higher than or equal to the flow temperature of the polymeric, polymerizable, and/or monomeric organic compound ( 14 ) and lower than the desorption temperature of the polymeric, polymerizable, and/or monomeric organic compound ( 14 ) for a period of time (t 1 ); and d) heating the starting material ( 10 ) to a temperature (T 2 ) which is higher than or equal to the sintering temperature of the particles ( 12 ) which can be sintered, optionally under the influence of a sintering pressure, for a period of time (t 2 ), thereby forming a sintering compound ( 22 ).

BACKGROUND OF THE INVENTION

The present invention relates to a method for connecting at least twocomponents using a sintering process.

Power electronics are used in many areas of technology. Especially inelectrical or electronic devices, in which great currents flow, the useof power electronics is indispensable. The current intensities that arenecessary in power electronics lead to a self-heating of the electricalor electronic components contained. In addition, the components of powerelectronics can be used at locations that are constantly subjected to anelevated temperature. Control devices in the automotive sector, whichare arranged directly in the engine compartment or in the transmissioncompartment, may be mentioned as examples. In this case, the controldevice is also exposed to a continual change of temperature, whereby theelectrical and/or electronic components contained undergo great thermalloading. Generally, temperature changes in a range up to a temperatureof 200° C. are usual. However, operating temperatures that go beyondthis are also increasingly being required. As a result, altogetherincreased requirements are being demanded of the reliability andfunctional dependability of electrical or electronic devices with powerelectronics.

Electrical or electronic components are usually joined together—forexample on a carrier substrate—by a connecting layer. Solderedconnections, for example lead-free soldered connections of tin-silver ortin-silver-copper, are known as such connecting layers. In cases ofhigher operating temperatures, lead-containing soldered connections canbe used. However, for reasons of environmental protection,lead-containing soldered connections are greatly restricted with respectto their permissible technical applications by legal regulations.Alternatively, lead-free hard solders are suitable for use at elevatedor high temperatures, in particular over 200° C. Lead-free hard soldersgenerally have a higher melting point than 200° C.

Sintered connections, which can already be processed at low temperaturesand are nevertheless suitable for operation at elevated temperatures,are also used. Such sintered connections offer the advantage of anincreased selection of electrical or electronic components that comeinto consideration as parts to be joined on account of the lowerprocessing temperature. Also advantageous in the case of sinteredconnections is that no creep takes place in the connecting layer, andconsequently no crack formation, whereby failure of an assembly havingsuch a connection can be reduced further.

Thus, the patent application DE 10 2007 046 901 A1 shows such sinteredconnections. To produce a sintered connection, a starting material inpaste form comprising readily decomposable silver compounds and silverflakes or nano silver is used. Furthermore, copper for example may becontained in the starting material.

The document EP 2 278 593 A1 discloses a sintered connection which isproduced from a paste that contains particles of a silver compound.

The document US 2008/0211095 A1 also discloses a semiconductor componentwhich has a connection between a semiconductor element and an electrodethat is formed by an electrically conductive adhesive.

The document U.S. Pat. No. 6,832,915 B2 also discloses a thermallyconductive adhesive connection between two components.

The document DE 10 2007 27 999 A1 also discloses a transfer film for thetransfer of a silver sintered layer.

The document DE 10 2004 019 567 B3 also describes a method for securingelectronic components, in which the components are secured on asubstrate by means of pressure sintering using a pasty layer.

The document JP 63258084 A also discloses a carrier film with asintering paste for joining electronic components.

U.S. Pat. No. 6,951,666 shows the production of different sinteredconnections. General possibilities for combining different startingelements are thereby described. Included among the elements mentioned asstarting elements are molecular metals, numerous metallic particles ofnano or micro size, coatings, solvents, additives, reducing agents,crystallization inhibitors, wetting agents and others.

SUMMARY OF THE INVENTION

The subject of the present invention is a method for connecting at leasttwo components using a sintering process, having the method steps of:

a) providing a starting material of a sintered connection, comprisingsinterable particles, comprising at least one metal or at least onemetal compound, and at least one polymeric, polymerizable and/ormonomeric organic compound, wherein the polymeric, polymerizable and/ormonomeric organic compound has a flow temperature that is greater thanor equal to the room temperature and less than the sinteringtemperature, and wherein the polymeric, polymerizable and/or monomericorganic compound also has a desorption temperature that is greater thanthe flow temperature and less than or equal to the sinteringtemperature;

b) arranging the starting material between two components to beconnected;

c) heating the starting material to a temperature T1, which is greaterthan or equal to the flow temperature of the polymeric, polymerizableand/or monomeric organic compound and less than the desorptiontemperature of the polymeric, polymerizable and/or monomeric organiccompound, for a time t1; and

-   -   d) heating the starting material to a temperature T2, which is        greater than or equal to the sintering temperature of the        sinterable particles, possibly under the effect of a sintering        pressure, for a time period t2, thereby forming a sintered        connection.

The method described above can make it possible in particular to carryout a sintering process particularly easily and thereby produce aparticularly stable and reliable sintered connection.

For this purpose, according to a method step a), the previouslydescribed method involves providing a starting material of a sinteredconnection, comprising sinterable particles, comprising at least onemetal or at least one metal compound, and at least one polymeric,polymerizable and/or monomeric organic compound, wherein the polymeric,polymerizable and/or monomeric organic compound has a flow temperaturethat is greater than or equal to the room temperature and less than thesintering temperature, and wherein the polymeric, polymerizable and/ormonomeric organic compound also has a desorption temperature that isgreater than the flow temperature and less than or equal to thesintering temperature.

Consequently, according to method step a), first a starting materialthat is intended in the further course of the method to form thesintered connection is provided. The starting material thereby comprisesa sintering base material, which after the sintering can represent theactual sintered connection or at least forms a large proportion of thesintered connection. This sintering base material may be in particularat least one metal or at least one metal compound. Furthermore, thestarting material comprises at least one polymeric, polymerizable and/ormonomeric organic compound. The polymeric, polymerizable and/ormonomeric organic compound may in this case serve the purpose of keepingthe sintering base material together, and thus allow the startingmaterial to be provided for example as a compact, for example moldable,for instance thermoplastic, molded body.

A polymeric organic compound may in this case be regarded for example,and not restrictively, as meaning a hydrocarbon-based compound that ispolymerized. Consequently, a polymerizable organic compound may forexample, and not restrictively, be understood as meaning such acompound, in particular a hydrocarbon-based compound, that can inparticular as a result of having specific functional groups be subjectedto a polymerization. An organic monomeric compound may furthermore beunderstood for example, and not restrictively, as meaning such acompound that likewise may be hydrocarbon-based, but need not have anygroups suitable for polymerization.

Such provision of a starting material of a sintered connection allowsthe starting material to be provided as a transportable and storablematerial, which can be applied at any time and without any specialeffort. In other words, the starting material is produced in advance andstored and is supplied for use immediately before carrying out themethod. This makes possible very dynamic and variable productionprocesses that can be adapted directly to the desired requirements.

In this case, the starting material may for example be provided as amaterial of a large surface area, from which a material part of asuitable size can be separated, for example punched out or cut out, ineach case before use. As a result, just one starting material can beprovided for a great range of applications, which can improve the costsfor the previously described method still further.

Furthermore, the starting material may be provided for instance by filmcasting or injection molding, initially for example as a particularlyflexible film, which keeps the handling requirements very low. As aresult, the starting material can be handled by conventional handlingsystems, which can allow particularly good incorporation of the startingmaterial in existing process peripherals.

In this case, during or after application of the starting material to acomponent or during arrangement of the starting material between thecomponents to be connected, it is possible, as described below, to adaptthe starting material optimally to potentially existing irregularitiesof the parts to be joined, such as for example substrate irregularitiesor component irregularities, so that a particularly intimate contactbecomes possible, which can also be accompanied by a particularly stablesintered connection.

In this case, the polymeric, polymerizable and/or monomeric organiccompound and the sintering base material or the at least one metal orthe at least one metal compound may in particular be made to match oneanother in such a way that the polymeric, polymerizable and/or monomericorganic compound has a flow temperature that is greater than or equal tothe room temperature and less than the sintering temperature of thesintering base material, and wherein the polymeric, polymerizable and/ormonomeric organic compound also has a desorption temperature that isgreater than the flow temperature and less than or equal to thesintering temperature of the sintering base material.

In the sense of the present invention, a flow temperature may beunderstood in particular as meaning a specific temperature or atemperature range from which the polymeric, polymerizable and/ormonomeric organic compound is flowable, and consequently can flow, thatis to say can remove itself from the joining zone of its own accord by aflowing process. In this case, a flow temperature may be understood inparticular as meaning a melting temperature or a melting range or aglass transition temperature or a glass transition range.

By such a selection of the sintering base material or the polymeric,polymerizable and/or monomeric organic compound, significant advantagesin conducting the process can be made possible.

In detail, it can be made possible by the selection in particular of thepolymeric, polymerizable and/or monomeric organic compound that thestarting material has a good adhesive force, and consequently can adherewell to the components to be joined, such as for instance a substrateand a component, in particular because of the polymeric, polymerizableand/or monomeric organic compound. In other words it is possible forinstance as a result of the polymeric, polymerizable and/or monomericorganic compound or a further auxiliary substance, such as for instancea solvent, for the starting material to have a suitable adhesivenessthat allows the starting material to adhere to the parts to be joined.This allows particularly good applicability, since the startingmaterial, once arranged, can remain securely in place. For example, suchan adhesive force or adhesiveness can be obtained at temperatures belowthe flow temperature, that is to say purely by way of example attemperatures in the range of less than or equal to 100° C.

In addition, the polymeric, polymerizable and/or monomeric organiccompound may serve the purpose of preventing cold fusing of theparticles and also of making it possible for the film material to beshaped.

After providing a starting material designed as described above,according to method step b) this starting material is arranged betweentwo components to be connected. This may take place for example in afully automated manner. In this case, the starting material may forexample be arranged between a substrate and an electronic component tobe secured on the substrate.

According to method step c), in a further step heating of the startingmaterial takes place to a temperature T1, which is greater than or equalto the flow temperature of the polymeric, polymerizable and/or monomericorganic compound and less than the desorption temperature of thepolymeric, polymerizable and/or monomeric organic compound, for a timet1. This method step allows an adhesive attachment of the startingmaterial to the components to be connected to be improved still further.In this case, such a temperature T1 may, depending on the chosenpolymeric, polymerizable and/or monomeric organic compound, already lieat temperatures of less than or equal to 100° C., for instance in arange of from greater than or equal to 30° C. to less than or equal to80° C. In detail, for example, an adhesiveness or an adhesive force ofthe polymeric, polymerizable and/or monomeric organic compound can befurther increased or such an adhesiveness can be formed in the firstplace by a flowability. Consequently, in this step it can be madepossible that the starting material firmly adheres between thecomponents to be connected, and consequently already forms anarrangement that already has good stability for the further sinteringoperation.

It can consequently be made possible by this method step that thestarting material is arranged at a desired position, and furthermoreremains there. As a result, particularly defined products can beobtained. In this case, by increasing the temperature beyond the flowtemperature of the polymeric, polymerizable and/or monomeric organiccompound, the starting material can be held in its position byparticularly stable forces. Consequently, an additional fixing medium isnot necessary, which allows the previously described method to be madeparticularly simple and inexpensive.

Furthermore, in particular in the flowable state, the polymeric,polymerizable and/or monomeric organic compound may serve as adispersing medium, in order to create a homogeneous starting material.

In addition, it can be made possible by a flowability of the polymeric,polymerizable and/or monomeric organic compound that the startingmaterial comes into close contact with the components to be connected,and otherwise, as a result of a softening, in particular reversiblesoftening, of the polymeric, polymerizable and/or monomeric organiccompound as a result of the temperature increase beyond the flowtemperature, a good adaptation between the layer of the startingmaterial and the parts to be joined is produced. In this way equally anintimate contact of the metallic compound or of the sintering basematerial with the components to be joined can be allowed. This maycontribute to a particularly stable arrangement being produced after asintering process, as is explained below.

Since, however, only a very small amount of polymeric, polymerizableand/or monomeric organic compound is necessary for an adhesiveness orclose contactability and the fixing of the starting material between theparts to be joined, it is possible to achieve the further advantage thatthe majority of the polymeric, polymerizable and/or monomeric organiccompound is removed from the joining zone as a result of flowability. Asa result, it can be achieved that a subsequent removal or desorption ofthe polymeric, polymerizable and/or monomeric organic compound from thejoining region does not cause a development or significant developmentof reaction gases that could possibly expand in the joint, and therebycounteract the formation of a material-bonded connection. Furthermore,for example, and depending on the desorption chosen, no oxygen isrequired, whereby the sintered connection can also take place with theexclusion of oxygen. This can avoid all the involved parts to be joinedundergoing a change or damage during a thermal treatment. In addition,the necessity of supplying gases or the necessity of removing gases canbe prevented. It is consequently not disadvantageous in the case of thepreviously described method that, particularly in the case ofconnections over a large surface area, the gas transport is limited bythe impermeability of the joining material, and consequently for examplein the case of production of a sealed connection the material is pressedby mechanical pressure, and consequently specifically inhibits transportof the gas. Consequently, to sum up, the disadvantages of removal ofsuch a matrix according to the prior art can be prevented by atemperature increase above the flow temperature of the polymeric,polymerizable and/or monomeric organic compound.

The time period t1, for which the temperature T1 is maintained, may inthis case be chosen in dependence on the starting material that isspecifically used. In particular, the time period should be chosen to belong enough for a sufficient flowability of the polymeric, polymerizableand/or monomeric organic compound to be realizable, and consequently forit to be possible for the aforementioned advantages to be achieved in aparticularly advantageous way.

In a further method step d), a previously described method involvesheating the starting material to a temperature T2, which is greater thanor equal to the sintering temperature of the sinterable particles,possibly under the effect of a sintering pressure, for a time period t2,thereby forming a sintered connection. In this method step,consequently, the actual sintered connection is produced.

In this case, the particles, for example chemically stabilizedparticles, are burned out, for instance until the joining temperature orsintering temperature is reached, so that the particles or releasedmetal atoms can come into direct contact with one another and with thematerial of the parts to be joined. Then, a connection that is stable athigh temperatures already forms at low temperatures as a result of soliddiffusion processes.

For this purpose, the starting material is heated on its own or togetherwith at least one joining region of the components to be connected to atemperature T2, for instance by a heating source or electromagneticradiation. In this case, the temperature T2 is greater than or equal tothe sintering temperature of the sinterable particles, that is to saythe particles comprising at least one metal or at least one metalcompound. In this case, the temperature T2 is maintained for apredetermined time period t2, which is sufficient for a stable sinteredconnection to be able to form.

In this case, the stability of the sintered connection formed can beincreased still further by the fact that the polymeric, polymerizableand/or monomeric organic compound also has a desorption temperature,that is to say a specific desorption temperature or a broad desorptiontemperature, that is to say a desorption range, that is greater than theflow temperature and less than or equal to the sintering temperature. Indetail, the polymeric, polymerizable and/or monomeric organic compoundis desorbed both by the sinterable particles and by the components to bejoined, that is to say in the sense of the present invention is removed.In this way it can be ensured that, after the forming of the sinteredconnection, it substantially comprises only the sintered particles orsintered products thereof. Therefore, the polymeric, polymerizableand/or monomeric organic compound does not disturb the stability of thesintered connection, as a result of which particularly stable productscan be obtained.

To sum up, the previously described method makes possible in particulara particularly simple and defined production of a sintered connectionbetween two components to be connected, with it also being possible forthe sintered connection that is formed to be particularly stable.

Within the scope of a refinement, the desorption temperature may be theboiling temperature, decomposition temperature or a reaction temperatureof the polymeric, polymerizable and/or monomeric organic compound withthe sinterable particles and/or with sintered particles. In particularin this refinement, it can be advantageously ensured that, in the caseof method step d), the polymeric, polymerizable and/or monomeric organiccompound can be removed completely, or without any residue, and thepolymeric, polymerizable and/or monomeric organic compound consequentlydoes not adversely influence the stability of the sintered connection.The fact that at least a certain proportion or advantageously a majorityof the polymeric, polymerizable and/or monomeric organic compound is nolonger arranged in the direct joining zone during method step d) meansthat even a vaporization, decomposition or combustion or a reaction,such as for instance an oxidation, by a constituent part of thesintering material, of the polymeric, polymerizable and/or monomericorganic compound arranged in particular outside the joining zone cannotcause the risk of a significant production of gas adversely influencingthe sintering process. The proportion of polymeric, polymerizable and/ormonomeric organic compound that is still located in the joining zone canin this case be in particular so small that there is no need for theoccurrence of any significant gas transport, which adversely influencesthe sintered connection that is forming or the stability of the sinteredconnection that has formed. Consequently, here even a removal by theaforementioned processes can be possible without any problem, or else itis possible for the polymeric, polymerizable and/or monomeric organiccompound to remain in the joining zone without adversely influencing thesintering process.

Within the scope of a further refinement, the sinterable particles maycontain silver, gold, platinum, palladium and/or copper, an organicmetal compound, in particular silver carbonate, silver lactate or silverstearate, a metal oxide, in particular silver oxide, or a mixturecomprising one or more of the aforementioned substances. Such particlesmay be particularly advantageously suitable for forming a highly stableand electrically conductive sintered connection. In this case, both thepure metals and corresponding metal compounds may be provided. Themetals may in this case allow in particular a material-bonded connectionbetween the parts to be joined to be obtained directly by a heat inputor an input of pressure, and thereby make a stable sintered connectionpossible. With respect to the metal compounds mentioned, they candecompose during a thermal treatment of the starting material, forinstance in a range of less than 300° C., to form the elemental metal,and form the sintered connection. When using the starting materialdescribed, electrical contacting can already take place with lowpressing pressures of the parts to be contacted, which consequently canallow mild reaction conditions, and consequently a simple andinexpensive method.

Within the scope of a further refinement, the polymeric, polymerizableand/or monomeric organic compound may comprise a polyolefin, inparticular comprising polyethylene and/or polypropylene, a polyethylenecopolymer, a polyketone or a mixture comprising one or more of theaforementioned substances. In particular, such polymeric, polymerizableand/or monomeric organic compounds may have the advantage that, withrespect to their flow temperature or with respect to their desorptionbehavior, they can be integrated well into a sintering process, inparticular in combination with the aforementioned sintering basematerials, that is to say in particular metals or metal compounds.Consequently, the aforementioned polymeric, polymerizable and/ormonomeric organic compounds may be particularly advantageously suitablefor taking up the sintering base material and also being removedsubstantially without any residue from a component to be joined by adesorption process. In addition, the aforementioned polymeric,polymerizable and/or monomeric organic compounds are stable underambient conditions, that is to say even in an oxidative atmosphereand/or in a moist atmosphere, so that particularly advantageousstorability can be made possible for the starting material, even over along period of time.

Within the scope of a further refinement, the polymeric, polymerizableand/or monomeric organic compound may form a matrix, in which thesinterable particles are embedded, or the polymeric, polymerizableand/or monomeric organic compound may take the form of a coating on thesinterable particles. These are particularly advantageous refinementsfor surrounding the sinterable particles by the polymeric, polymerizableand/or monomeric organic compound.

With respect to a matrix in which the sinterable particles are embedded,it is thus possible to produce a molded body that can be adapted in alldimensions to the desired application area. In detail, such a body canbe adapted in its length, width and height to the components to bejoined. As a result, the method can be made even more simple andinexpensive. For example, in this way a moldable composition that canadhere to itself, and in particular can be handled well, can beproduced. In this case, such a starting material may for instance beproducible by melting the polymeric, polymerizable and/or monomericorganic compound followed by mixing with the sintering base material andfinal cooling.

With respect to a coating, the proportion of the polymeric,polymerizable and/or monomeric organic compound can be kept particularlylow, so that the composition leaving the joining region when there is anincrease in temperature beyond the flow temperature of the polymeric,polymerizable and/or monomeric organic compound can be kept particularlysmall. Consequently, the method can be carried out in a particularlytime-saving manner. In this case, the coating of the particles mayalready be applied during the production of the particles, in particularin order to prevent a reaction of the sinterable particles with oneanother, for instance cold fusing. For example, the metal particles,which are produced for example as silver particles by a gas-phasedeposition or precipitation in a solvent, are coated by the solventcomprising a corresponding coating material, for example as asurface-active material. After removal of the solvent, for example, thestarting materials comprising the sinterable particles, which forinstance as a powder are in a form that can be handled, can be obtainedwith the coating, in particular chemically or physically bonded coating.

In these refinements, the starting material can thus be applied, orbrought into contact with the components to be joined, as a powder or asa pressed body of the powder or else as a paste with a solvent by meansof methods that are known in principle, such as for instance placementof the green body. Also in these refinements, the viscosity of thepolymeric, polymerizable and/or monomeric organic compound can be set bymeans of a temperature control, so that the viscosity is controllable bya temperature setting and in that case a temperature increase can havethe effect that the compound can be removed from the joint, inparticular by capillary forces, and in a further method step can becompletely removed or desorbed.

Within the scope of a further refinement, the starting material may beapplied to at least one component to be connected by printing, doctorblading or dispensing. These are particularly simple andwell-established processes for applying the starting material to atleast one of the components to be connected. In these refinements, aparticularly precise and highly accurate arrangement of the startingmaterial is possible, which can make highly stable sintered connectionspossible even in components of small dimensions. In this case, thestarting material may be applied both to only one of the components tobe connected or to both starting components to be used.

Within the scope of a further refinement, the starting material may havea transfer layer, which is arranged between at least two protectivelayers, in particular comprising a polymeric, polymerizable and/ormonomeric organic compound. For example, the transfer layer may comprisethe sintering base material or the sinterable particles and possibly thepolymeric, polymerizable and/or monomeric organic compound. In thiscase, the polymeric, polymerizable and/or monomeric organic compound ofthe transfer layer may be the same compound as the compound of theprotective layers. Alternatively, it is possible to dispense with thepolymeric, polymerizable and/or monomeric organic compound in thetransfer layer, which may enclose the sinterable particles directly, forinstance as a coating or as a matrix, so that the sinterable particlesare only surrounded by the protective layers comprising a polymeric,polymerizable and/or monomeric organic compound. In this refinement, thestarting material can be handled particularly easily and nevertheless bearranged very precisely at the desired location. In this case, thetransfer layer is protected particularly well from external influences,and as a result is particularly storable.

In this case, arranging the starting material on one of the componentsto be joined can be realized by way of example, and not restrictively,by the protective layers being removed before or during method step b).In this case, as an example, it may be that first a protective layer isremoved and the exposed side of the transfer layer arranged on thecomponent, and then the further protective layer is removed. In thisway, the starting material may have in particular a transfer layer thatis surrounded on two opposite sides by the protective layer. In thiscase, the protective layers may also be formed in such a way thatsubstantially the entire transfer layer is surrounded by protectivelayers. It may be that this can be realized by providing more than twoprotective layers and also by a corresponding form of the at least twoprotective layers.

In this case it is possible in this refinement in particular to dispensewith applying the sintering base material by printing, dispensing ordoctor blading with a subsequent thermal treatment for drying theapplied layer. Therefore, in this refinement in particular, thepreviously described method can do without some steps in the process,which can save production costs of the components to be produced andalso time for producing such components.

Within the scope of a further refinement, the protective layers maycomprise polyethylene terephthalate. In particular, polyethyleneterephthalate may serve as a stable protective layer, in order toprotect the transfer layer reliably from external influences, such asfor example mechanical influences. In addition, it is inert with respectto the materials occurring in the transfer layer, so that no adverseinfluencing of the transfer layer is to be expected, even over aprolonged period of time. Furthermore, polyethylene terephthalate can beobtained inexpensively, so that also in this refinement the method canbe realized particularly inexpensively.

Within the scope of a further refinement, the starting material may beprovided in the form of a paste, a powder, granules or a film. Suchforms of the starting material can be handled easily, inexpensively andby known methods, so that in these refinements in particular the methodcan be possible particularly simply and inexpensively. In addition,storage is unquestionably possible, so that the advantages with respectto production in advance and use or provision immediately before themethod are possible without any problem.

Within the scope of a further refinement, the polymeric, polymerizableand/or monomeric organic compound may be discharged or removed during orafter method step c). In this refinement, the effect occurring inprinciple as a result of flowability of the polymeric, polymerizableand/or monomeric organic compound, whereby the compound already leavesthe joining zone by flowing away, can be further enhanced or assisted.

With respect to discharging of the polymeric, polymerizable and/ormonomeric organic compound, one or a plurality of collecting containersmay be provided for example, such as for instance cavities, into whichthe flowable compound can be discharged, that is to say guided. For thispurpose, channels may be provided for example, arranged in such a waythat the compound flows in a flowable state, or the collectingcontainers may themselves be directly arranged in such a way that theflowable compound flows in there. In this case, the collectingcontainers may for instance be arranged directly alongside thecomponents to be joined and the channels may for instance reach into thejoining region.

With respect to removal of the polymeric, polymerizable and/or monomericorganic compound, the flowable compound may for example be taken up andcarried away by means of a suitable device.

Sponge-like devices or capillary bundles, which can take up or suck inthe compound by means of capillary forces, may for example be used forthis purpose. This can bring about particularly low-stress removal ofthe compound, and as such not adversely influence the sintering process.

Within the scope of a further refinement, the polymeric, polymerizableand/or monomeric organic compound may contain at least one additive thatreacts with the sinterable particles, in particular with the organicmetal compound, while reducing the sintering temperature. In thisrefinement in particular, a particularly low-stress method can be madepossible, since low temperatures may already be sufficient for asintering process. As a result, even such components that should not beexposed to temperatures that are all that high can be connected to oneanother. In addition, polymeric, polymerizable and/or monomeric organiccompounds that have a relatively low desorption temperature can also beused, which can for example increase the selection of such compounds,including with respect to conventional polymers. Oxidizable organiccompounds, such as for instance fatty acids, for example stearic acid orlauric acid, in particular in combination with the aforementionedsintering base materials, such as for instance silver, may be mentionedas exemplary and nonrestrictive examples of such additives.

Within the scope of a further refinement, it is possible to produce asintered connection that has an electrical conductivity of from greaterthan or equal to 30 MS/m to in particular less than or equal to 45 MS/m,in particular from greater than or equal to 36 MS/m to in particularless than or equal to 44 MS/m, and/or to produce a sintered connectionthat has a thermal conductivity of from greater than or equal to 200W/mK to less than or equal to 300 W/mK, in particular from greater thanor equal to 220 W/mK to less than or equal to 275 W/mK. Such sinteredconnections in particular may be customary for a large number ofelectronic components that are possibly used in power electronics. Suchconductivities may for example be achievable by the use of thepreviously described sintering base materials.

Within the scope of a further refinement, an electronic component may beused as one of the components to be connected and a substrate, forinstance comprising a copper compound, may be used as another of thecomponents to be connected. In this refinement, electronic components inparticular may be applied to the corresponding substrates. In the caseof such applications in particular, a very stable connection, which isadditionally electrically conductive, is beneficial. Therefore, in thisrefinement in particular it is of advantage that the sintered connectioncan be positioned highly accurately, and furthermore no gas transportingprocesses have a significant adverse influence on the forming of astable connecting layer. For example, in this refinement in particularan electronic component of power electronics can be produced.

With regard to further technical features and advantages of the methodaccording to the invention, reference is hereby made explicitly to theexplanations in connection with the use according to the invention, thefigures and the description of the figures.

The subject of the present invention is also a use of a method refinedin the way described above for producing an electronic component, inparticular an electronic circuit. In the case of this use, an electroniccomponent or an electronic circuit can consequently be produced by acomponent, in particular an electronic component, being secured on asubstrate by a sintering process. In this case, power semiconductors orintegrated circuits may for example be secured as electronic componentson the substrate by the sintered connection. In particular, thepreviously described method can be used in the case of components to bejoined that should only be exposed to low thermal loading, since thetemperatures that are necessary for flowability or desorption of thepolymeric, polymerizable and/or monomeric organic compound and arenecessary for sintering the sintering base material can likewise be keptlow in the case of a previously described method on account of theselection of the starting material. For example, in this refinementsilicon chips or silicon carbide components, which can withstandtemperatures of for example 250° C. or 350° C., respectively, can bejoined without any problem, such as for example in the so-called “dieattach” process.

In principle, this refinement consequently comprises a use of thepreviously described method in the region of electronic constructiontechnology or connection technology, in particular as a low-temperaturesintering technique. For example, diffusion soldering or activesoldering can be replaced by the previously described method.

With regard to further technical features and advantages of the useaccording to the invention, reference is hereby made explicitly to theexplanations in connection with the method according to the invention,the figures and the description of the figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages and advantageous refinements of the subjectsaccording to the invention are illustrated by the examples and drawingsand are explained in the description that follows. It should be notedhere that the examples and drawings only have a descriptive characterand are not intended to restrict the invention in any form. In them:

FIGS. 1 a, 1 b and 1 c show a schematic representation of production ofone embodiment of a starting material for a method according to theinvention;

FIGS. 2 a, 2 b and 2 c show a schematic representation of a methodaccording to the invention using a starting material according to FIG.1; and

FIGS. 3 a, 3 b and 3 c show a schematic representation of a methodaccording to the invention using a further refinement of a startingmaterial.

DETAILED DESCRIPTION

In FIG. 1 c, a starting material 10 for a method according to theinvention for connecting at least two components using a sinteringprocess is shown. In the refinement according to FIG. 1 c, the startingmaterial 10 of a sintered connection comprises sinterable particles 12,comprising at least one metal or at least one metal compound.Furthermore, the starting material 10 comprises at least one polymeric,polymerizable and/or monomeric organic compound 14, which according toFIG. 1 is arranged as a coating on the sinterable particles 12. In thiscase, the sinterable particles 12 and/or the polymeric, polymerizableand/or monomeric organic compound 14 are chosen in such a way that thepolymeric, polymerizable and/or monomeric organic compound 14 has a flowtemperature that is greater than or equal to the room temperature, thatis to say according to the invention is greater than or equal to 22° C.,and less than the sintering temperature of the sinterable particles, andthe polymeric, polymerizable and/or monomeric organic compound 14 alsohaving a desorption temperature that is greater than the flowtemperature and less than or equal to the sintering temperature.

In this case, an exemplary production process for the starting material10 is shown in FIG. 1. In FIG. 1 a, a sinterable particle 12 that hasbeen produced in a solvent 16 is shown. The sinterable particle 12 mayfor example be a silver particle. In FIG. 1 b, it is also shown that acoating of a polymeric, polymerizable and/or monomeric organic compound14 is arranged on the sinterable particle 12. This coating may beproduced by the polymeric, polymerizable and/or monomeric organiccompound 14 being added to the solvent 16, for example dissolved ordispersed. By way of example, a colophony resin, which can serve as afluxing agent, may be used as the polymeric, polymerizable and/ormonomeric organic compound 14. This has the advantage with respect tothe method according to the invention that it is soft and adhesive atslightly elevated temperatures of well below 100° C., but in the furthercourse of conducting the process evaporates virtually without anyresidue by decomposing and can be produced as a preform at 25° C. Thecompleted starting material 10, obtained as described above byevaporating the solvent, is shown in FIG. 1 c.

Such a starting material 10 may be arranged directly between twocomponents 18, 20 to be connected, as is shown in FIG. 2 a. In thiscase, the starting material 10 may be applied to at least one component20 to be connected by printing, doctor blading or dispensing. Forexample, the component 20 may be a substrate, whereas the component 18may be an electronic component, such as for instance a powersemiconductor component.

In FIG. 2 b, a first thermal treatment step is shown. In detail, a stateafter a method step comprising heating of the starting material 10 to atemperature T1, which is greater than or equal to the flow temperatureof the polymeric, polymerizable and/or monomeric organic compound 14 andless than the desorption temperature of the polymeric, polymerizableand/or monomeric organic compound 14, for a time t1 is shown in FIG. 2.This results in part of the polymeric, polymerizable and/or monomericorganic compound 14 being removed from the joining zone and arrangingitself on the component 20 or wetting the surface of the component 20.In this case, the polymeric, polymerizable and/or monomeric organiccompound 14 can be discharged or removed during or after this methodstep of the first heat treatment.

In FIG. 2 c, furthermore, a formed sintered connection 22 of the twocomponents 18, 20 is shown. Such a sintered connection 22 is formed bysintered sinterable particles 12, by a further method step involvingheating the starting material 10 to a temperature T2, which is greaterthan or equal to the sintering temperature of the sinterable particles10, possibly under the effect of a sintering pressure, for a time periodt2, thereby forming a sintered connection 22. For example when usingsilver as sinterable particles 12, the sintered connection 22 may havean electrical conductivity of from greater than or equal to 30 MS/m toin particular less than or equal to 45 MS/m, in particular from greaterthan or equal to 36 MS/m to in particular less than or equal to 44 MS/m,and/or may have a thermal conductivity of from greater than or equal to200 W/mK to less than or equal to 300 W/mK, in particular from greaterthan or equal to 220 W/mK to less than or equal to 225 W/mK.Furthermore, sintering may by way of example take place at a sinteringpressure of less than or equal to 10 MPa, for example of less than orequal to 1 MPa and/or at a sintering temperature in a range of less thanor equal to 300° C., for example less than or equal to 250° C.

In FIGS. 3 a to 3 c, a further refinement of a starting material 10 anda method performed with it is shown. In the refinement according to FIG.3 a, the polymeric, polymerizable and/or monomeric organic compound 14forms a matrix, in which the sinterable particles 12 are embedded. Inthis case, the polymeric, polymerizable and/or monomeric organiccompound 14 is arranged together with the sinterable particles 12 in atransfer layer 24, for instance as an adhesive film. The transfer layer24 is in this case arranged between at least two protective layers 26,28, in particular comprising a polymeric, polymerizable and/or monomericorganic compound 30.

In order to form a sintered connection 22, it may be the case that firsta protective layer 28 is removed and the starting material 10 istransferred to the first component 20. After the removal of the secondprotective layer 26 or of all the protective layers still present, thesecond component 18 is correspondingly positioned on the startingmaterial 10 or on the transfer layer 14. In this case, reference is madehere, and possibly also in respect of further method steps, to thestarting material 10, even though sometimes only part of the startingmaterial is present, which however can be included in the sense of theinvention by referring to starting material 10. This state is shown inFIG. 3 b.

This may be followed by a first thermal treatment, in which thepolymeric, polymerizable and/or monomeric organic compound 14 melts, andfor example may become adhesive. In the sintering process, thepolymeric, polymerizable and/or monomeric organic compound 14 can beremoved and, furthermore, as a result of the elevated temperature, thesintered sinterable particles can form a sintered connection 22, as isshown in FIG. 3 c.

1. A method for connecting at least two components (18, 20) using a sintering process, comprising: a) providing a starting material (10) of a sintered connection (22), comprising sinterable particles (12), comprising at least one metal or at least one metal compound, and at least one polymeric, polymerizable and/or monomeric organic compound (14), wherein the polymeric, polymerizable and/or monomeric organic compound (14) has a flow temperature that is greater than or equal to room temperature and less than a sintering temperature of the sinterable particles, and wherein the polymeric, polymerizable and/or monomeric organic compound (14) also has a desorption temperature that is greater than the flow temperature and less than or equal to the sintering temperature; b) arranging the starting material (10) between two components (18, 20) to be connected; c) heating the starting material (10) to a temperature T1, which is greater than or equal to the flow temperature of the polymeric, polymerizable and/or monomeric organic compound (14) and less than the desorption temperature of the polymeric, polymerizable and/or monomeric organic compound (14), for a time t1; and d) heating the starting material (10) to a temperature T2, which is greater than or equal to the sintering temperature of the sinterable particles (12), for a time period t2, thereby forming a sintered connection (22).
 2. The method as claimed in claim 1, wherein the desorption temperature is a boiling temperature, a decomposition temperature or a reaction temperature of the polymeric, polymerizable and/or monomeric organic compound (14) with the sinterable particles and/or with sintered particles (12).
 3. The method as claimed in claim 1, wherein the sinterable particles (12) contain silver, gold, platinum, palladium and/or copper, an organic metal compound, a metal oxide, or a mixture comprising one or more of the aforementioned substances.
 4. The method as claimed in claim 1, wherein the polymeric, polymerizable and/or monomeric organic compound (14) comprises a polyolefin, a polyethylene copolymer, a polyketone or a mixture comprising one or more of the aforementioned substances.
 5. The method as claimed in claim 1, wherein the polymeric, polymerizable and/or monomeric organic compound (14) forms a matrix, in which the sinterable particles (12) are embedded, or wherein the polymeric, polymerizable and/or monomeric organic compound (14) takes the form of a coating on the sinterable particles (12).
 6. The method as claimed in claim 1, wherein the starting material (10) is applied to at least one component to be connected by printing, doctor blading or dispensing.
 7. The method as claimed in claim 1, wherein the starting material (10) has a transfer layer (24), which is arranged between at least two protective layers (26, 28).
 8. The method as claimed in claim 7, wherein the protective layers (26, 28) are removed before or during method step b).
 9. The method as claimed in claim 7, wherein the protective layers (26, 28) comprise polyethylene terephthalate.
 10. The method as claimed in claim 1, wherein the starting material (10) is provided in the form of a paste, a powder, granules or a film.
 11. The method as claimed in claim 1, wherein the polymeric, polymerizable and/or monomeric organic compound (14) is discharged or removed during or after method step c).
 12. The method as claimed in claim 1, wherein the polymeric, polymerizable and/or monomeric organic compound (14) contains at least one additive that reacts with the sinterable particles (12), while reducing the sintering temperature.
 13. The method as claimed in claim 1, wherein a sintered connection (22) that has an electrical conductivity of from greater than or equal to 30 MS/m is produced, and/or wherein a sintered connection (22) that has a thermal conductivity of from greater than or equal to 200 W/mK to less than or equal to 300 W/mK is produced.
 14. The method as claimed in claim 1, wherein an electronic component is used as one of the components to be connected and a substrate is used as another of the components (20) to be connected.
 15. The use of a method as claimed in claim 1 for producing an electronic component.
 16. The method as claimed in claim 1, wherein method step d) includes heating the starting material (10) to a temperature T2 under the effect of a sintering pressure.
 17. The method as claimed in claim 1, wherein the sinterable particles (12) contain silver, gold, platinum, palladium and/or copper, an organic metal compound, comprising silver carbonate, silver lactate or silver stearate, a metal oxide, comprising silver oxide, or a mixture comprising one or more of the aforementioned substances.
 18. The method as claimed in claim 1, wherein the polymeric, polymerizable and/or monomeric organic compound (14) comprises a polyolefin, comprising polyethylene and/or polypropylene, a polyethylene copolymer, a polyketone or a mixture comprising one or more of the aforementioned substances.
 19. The method as claimed in claim 1, wherein the starting material (10) has a transfer layer (24), which is arranged between at least two protective layers (26, 28), comprising a polymeric, polymerizable and/or monomeric organic compound.
 20. The method as claimed in claim 1, wherein the polymeric, polymerizable and/or monomeric organic compound (14) contains at least one additive that reacts with the organic metal compound, while reducing the sintering temperature.
 21. The method as claimed in claim 1, wherein a sintered connection (22) that has an electrical conductivity of from greater than or equal to 30 MS/m to less than or equal to 45 MS/m is produced, and/or wherein a sintered connection (22) that has a thermal conductivity of from greater than or equal to 200 W/mK to less than or equal to 300 W/mK is produced.
 22. The method as claimed in claim 1, wherein a sintered connection (22) that has an electrical conductivity of from greater than or equal to 36 MS/m to less than or equal to 44 MS/m is produced, and/or wherein a sintered connection (22) that has a thermal conductivity of from greater than or equal to 220 W/mK to less than or equal to 275 W/mK is produced.
 23. The method as claimed in claim 1, wherein an electronic component is used as one of the components to be connected and a substrate, comprising a copper compound, is used as another of the components (20) to be connected. 